Magneto-generator ignition system

ABSTRACT

An energy storage and discharge control circuit for use with the ignition system of an internal combustion engine. During the time interval when the breaker points are opening, a capacitor is charged with a voltage through a polarity determining diode network. When the voltage has increased to a certain level, a semiconductor switch is turned on, allowing the charge on the capacitor to be directed through the primary winding of the ignition coil to increase the voltage induced in the secondary of the coil and to control the voltage-time characteristic of the energy impulse which is applied to the engine&#39;&#39;s spark plug.

United States Patent [191 Kuehn, III

[4 1 May 20, 1975 1 1 MAGNETO-GENERATOR IGNITION SYSTEM [75] Inventor:Andrew Kuehn, 111, St. Paul, Minn.

[73] Assignee: Systematics, Inc., St Paul, Minn.

[22] Filed: Sept. 6, 1973 [21] Appl. No.: 394,636

[52] US. Cl.... 123/148 R; 123/149 R; 315/209 CD Primary ExaminerCharles.1. Myhre Assistant ExaminerRonald B. Cox

[57] ABSTRACT An energy storage and discharge control circuit for usewith the ignition system of an internal combustion engine. During thetime interval when the breaker points are opening, a capacitor ischarged with a voltage through a polarity determining diode network.When the voltage has increased to a certain level, a semiconductorswitch is turned on, allowing the charge on the capacitor to be directedthrough the primary winding of the ignition coil to increase the voltageinduced in the secondary of the coil and to control the voltage-timecharacteristic of the energy impulse which is applied to the enginesspark plug.

2 Claims, 4 Drawing Figures MAGNETO-GENERATOR IGNITION SYSTEM BACKGROUNDOF THE INVENTION This invention relates generally to an improvement inthe ignition system of internal combustion engines, particularlymulti-cylinder engines, such as are commonly employed in snowmobiles andother vehicles, and more specifically to a novel ignition energy storageand discharge network for producing an energy pulse of predeterminedcharacteristics which improves the performance of such an engine.

A well-known form of ignition circuit for a multiple cylinder, two-cycleinternal combustion engine is the combination of a magneto-generator andignition coil for developing a high tension voltage across the gap of aspark plug. The magneto-generator generally comprises a coil orcombination of coils cooperating with one or more magnets mounted on arevolving flywheel. The movement of the magnets with respect to thecoils induces a current therein. At a point in time of the compressionphase of the operational cycle, which point is determined by the openingofa set of cam operated breaker points, this current flow is suddenlydiverted into the primary winding of the ignition coil, causing a highvoltage to be induced in the secondary winding thereof and ultimatelyacross the gap in the spark plug. The voltage is sufficiently high tobreak down the air/fuel mixture in the gap and produce a hot spark forignition of the mixture present in the cylinder. In thisconventionalsystem, a capacitor is connected in parallel with thebreaker points to prevent sparking and attendant pitting of the pointsas well as to electrically tune the magneto-generator circuit tomaximize the energy transfer to the spark plug.

The present ignition circuits suffer from several deficiencies. First,the time rate of increase of the high tension voltage is normally slowerthan desired for firing a spark plug, especially when the plug ispartially fouled or shorted. In that condition, the somewhat slowvoltage rise rate causes the plug to fire with less stored energy thandesired in the secondary winding of the ignition coil, thus reducing thesize of the initial capacitive discharge across the plug gap. Secondly,the presently available systems tend to allow a prolonged current flowthrough the plug gap following the initial breakdown which does not addappreciably to the ignition of the air/gas mixture. Further, because ofthe inductive nature of the ignition coil, the initial rise of voltageacross the breaker points may be extremely rapid, limited only by thepresence of the capacitor connected in parallel therewith, thus causingarcing or sparking at the points and attendant wear and pitting.

SUMMARY OF THE INVENTION The present invention obviates thesedeficiencies. In accordance with the essential features of the presentinvention, means are provided to temporarily store the energy which isbeing transferred from the magnetogenerator, and at a precise point intime determined by a solid-state switch, this stored energy is releasedinto the primary winding of the ignition coil in the form of an energypulse which has predetermined rise and fall time characteristics.

More specifically, the circuit of the present invention includes acapacitor connected in series between the coils of the magneto-generatorand the primary winding of the ignition coil. A diode network isconnected in circuit with the capacitor and the magneto-generator coilso that the capacitor will be charged with a predetermined polaritywithout the need for current to flow through the primary winding of theignition coil. Then,

a solid-state discharge control circuit is provided which, whentriggered on, permits a controlled current pulse to flow through theignition coil for the purpose of inducing a high tension voltage acrossthe gap of the spark plug.

It is accordingly an object of the present invention to provide aninexpensive circuit for improving and controllably modifying theoperational characteristics of a conventional magneto-generator ignitionsystem for an internal combustion engine, particularly with multiplecylinders.

Another object of the invention is to provide a circuit modification forimproving the performance characteristics of such internal combustionengines.

Still another object of the present invention is to provide a simple,inexpensive electronic circuit which is easily installed and whichimproves the operating characteristics of such engines.

These and other objects of the invention will become apparent to thoseskilled in the art upon a study of the following detailed description ofthe accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a block diagramrepresentation of the preferred embodiment of the present invention;

FIG. 2 is an electrical schematic showing one arrangement forimplementing the block diagram of FIG.

FIG. 3 is a diagram showing the waveform of the generated voltage andthe affect of point closure thereon; and

FIG. 4 illustrates a suppression circuit suitable for use in the circuitof FIG. 2 for removing negative-going spikes which might cause off-cyclefiring.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the blockdiagram of FIG. 1, there is shown a conventional ignition system for atwocylinder, two-cycle internal combustion engine incorporating thepresent invention. Specifically, there is shown enclosed by the dashedline box 10, the solidstate energy storage and discharge circuit whichhas been devised to improve the performance characteristics of such anignition system.

The overall system includes a flywheel 12 which is secured to the driveshaft 14 and which is provided with a permanent magnet 16 integrallymounted therein, as is conventional. In close proximity to the peripheryof the flywheel 12 there is positioned a pair of magnetogenerator coilsI8 and 20, with one such coil being provided for each cylinder in theengine. When the permanent magnet 16 moves past these coils, anelectrical current will be induced in the coils. Each of the coils l8and 20 has one of its terminals connected in common to a grounded bus22. In the circuit shown in FIG. 1, the circuit components positionedabove this grounded bus 22 are associated with a first cylinder of a twocylinder engine (hereinafter referred to as cylinder A) and the circuitcomponents located below the grounded bus 22 are associated with thesecond cylinder (hereinafter referred to as cylinder B).

Connected in parallel with the magneto-generator coil 18 between groundbus 22 and a conductor 24 is a set of breaker points 26 for cylinder A.Similarly, connected in parallel with the magneto-generator coil betweenthe ground bus 22 and a conductor 28 is a second set of breaker points30 associated with cylinder B of the engine. In each instance, breakerpoints or contacts 26 and 30 are operated by a revolving cam (not shown)secured to the drive shaft as is conventional. Points 26 and 30 operatein complementary fashion. In other words, when the breaker points 26 areopen, points 30 will be closed, and vice-versa. In order to reducearcing across the breaker points 26 upon opening, a capacitor 32 isconnected between ground conductor 22 and the outer conductor 24. Asecond capacitor 34 is connected between ground bus 22 and conductor 28for a similar purpose.

In prior art magneto-generator type ignition systems, the primarywinding of the ignition coil (autotransformer) is connected directly inparallel with the breaker points between the grounded bus 22 and theouter conductors 24 and 28. As long as the breaker points remain closed,the ,coils l8 and 20 are shorted and a relatively high circulatingcurrent flows in these coils. When the breaker points open, thiscirculating current will be diverted through the primary winding of theinduction coil and will cause a relatively high voltage to be developedacross the secondary winding thereof and applied across the gap of thespark plugs.

In FIG. 1, the ignition coil for cylinder A is identified by numeral 36and that for cylinder B is identified by numeral 38. In implementing thepresent invention in a conventional ignition system, the leads 24 and 28normally connected to the outer terminals 40 and 42 of the' ignitioncoils 36 and 38 respectively are severed, as is the ground bus 22 whichis connected to the common terminal 44 of the primary windings of coils36 and 38. Inserted in series between the conductor 24 and the terminal40 is an energy storage device, here shown as capacitor 46. Similarly, acapacitor 48 is connected in series between the conductor 28 and theterminal 42 on transformer 38. A discharge control circuit 50, which isdescribed more fully hereinbelow, is connected between the conductors 24and 28 at junctions 52 and 54 respectively. Connected in parallel withthe primary winding of ignition coil 36 is a polarity directing circuit56. A similar circuit 58 is connected in parallel with the primarywinding of the ignition coil 38.

The spark plug for cylinder A is connected across the secondary windingof ignition coil 36 and is shown in FIG. 1 at 60. Likewise, the sparkplug associated with cylinder B is connected across the secondarywinding of ignition coil 38 and is shown at 62.

OPERATION FIGURE 1 In order to understand the operation of the circuitof FIG. 1, let it be assumed that the breaker points 26 are justbeginning to open and that the breaker points 30 are closed. Immediatelyprior to the opening of the breaker points 26, the current induced inthe magnetogenerator coil 18 had been circulating through the points 26and no current was being delivered to the other portions of the circuitassociated with cylinder A. Upon opening of the breaker points 26, thiscirculating current in coil 18 is diverted through conductor 24,capacitor 46 and the polarity directing device 56 and through groundconductor 22 back to the grounded terminal of the coil ofmagneto-generator 18. The affect of this current is to cause thecapacitor 46 to become charged with a voltage having the polarity asindicated by the markings adjacent thereto. As the capacitor 46 isinitially charging, the discharge control circuit 50 acts as an opencircuit whereas the polarity directing device 56 acts as a shortcircuit, preventing any current from flowing into the primary winding ofthe ignition coil 36.

The discharge control circuit has a characteristic such that when thevoltage or charge developed on the capacitor 46 reaches a predeterminedlevel, the discharge control circuit will be rendered conductive. Oncethe discharge control circuit 50 is conducting, a current will flow fromthe positively marked terminal of capacitor 46, through the dischargecontrol circuit 50, through conductor 28, through the closed points 30associated with cylinder B, through the ground conductor 22 to thejunction 44 and thence through the primary winding of induction coil 36and the junction 40 back to the negatively marked terminal of thecapacitor 46, thus discharging the capacitor. The current flowingthrough the primary winding of the ignition 36 induces a very highvoltage across its secondary winding caus' ing the air/gas mixtureexisting between the gap in the spark plug 60 to break down capacitivelyand ignite the fuel mixture within the cylinder. It is to be noted thatduring the time that the capacitor 46 is discharging, the polaritydirecting device 56 will be in a blocking condition such that all of thedischarge current will be available to the primary winding of thetransformer 36.

In a similar fashion, if it is now assumed that breaker points 30 arecommencing to open and that the points 26 are closed, it will be seenthat the circulating current from the magneto-generator coil 20 will bediverted through conductor 28, the capacitor 48, the polaritydetermining network 58, and the grounded bus 22 so as to cause thecapacitor 48 to charge up in a direction indicated by the polaritymarkings thereon. When the charge on capacitor 48 exceeds apredetermined threshold determined by the characteristics of thedischarge control circuit 50, the discharge control circuit 50 will berendered conductive and the capacitor 48 will begin to discharge throughcircuit 50, conductor 24, points 26, ground bus 22, the primary windingof ignition coil 38 back to the negative terminal of the capacitor 48.The effect of this discharge current is to cause a substantial voltageto be developed across the secondary winding of the coil 38 so as tobreak down the air/fuel mixture in the gap of spark plug 62 associatedwith cylinder B and ignite the mixture within the cylinder.

Thus, it can be seen that by connecting the discharge control circuit 50in circuit with the breaker points 26 and 30, only one such dischargecontrol circuit is needed to implement the improved ignition system fora two-cylinder internal combustion engine.

Illustrated in FIG. 2, is one arrangement for implementing the systemdiagram of FIG. 1 with commercially available electronic components. InFIG. 2, the various circuit components described functionally in FIG. 1have been given the same identifying numerals as utilized in FIG. 1. Asis illustrated, the discharge control circuit 50 comprises a resistivevoltage divider including resistors 64 and 66 connected in series acrossthe conductors 24 and 28. Connected in parallel with the resistor 66 isa capacitor 68. The discharge control circuit also includes asemi-conductor switching device, here shown as a Triac 68. The controlor gate electrode of the Triac 68 is connected to a junction 70 betweenthe resistors 64 and 66. The input and output electrodes of the Triac 68are connected in series with an inductor 72 between the conductors 24and 28. A pair of oppositely poled diodes 74 and Y76 are connectedtogether across the inductor 72 and the common terminal thereof isconnected to the center tap on the inductor 72.

The polarity directing circuits 56 and 58 each include a seriescombination of a resistor and a diode. More particularly, the anode of adiode 78 is connected by a conductor to the junction point 40, while thecathode thereof is connected through a resistor 80 to the ground bus 22.Similarly, the polarity directing network 58 includes a diode 82 havingits anode connected by a conductor to the junction 42 and its cathodeconnected through a resistor 84 to a junction on the ground bus 22.

OPERATION FIGURE 2 The operation of the circuit of FIG. 2 will beconsidered with the situation assumption made that the Triac 68 isnonconducting and that the breaker points 26 have just opened whereasthe breaker points 30 are closed. As was explained in connection withFIG. 1, upon opening of the points 26, the circulating existing in themagneto-generator coil 18 will be diverted through conductor 24, throughcapacitor 46, through the diode 78 and resistor 80 and through theground bus 22 back to the ground terminal of the coil 18. With thebreaker points 30 closed, the conductor 28 will be at ground potentialand a voltage proportional to the voltage developing on capacitor 46will appear at the junction point 70 of the voltage divider comprised ofresistors 64 and 66. Thus, the capacitor 68 connected in parallel withthe resistor 66 will maintain this voltage and when the potentialappearing at junction 70 exceeds the threshold value for initiatingconduction in Triac 68, it will do so, causing a discharge current toflow from the capacitor 46 through the inductor 72, through the Triac68, through conductor 28 and the closed breaker points 30 and thencethrough the grounded bus 22 to the junction 40 back to the negativeterminal of the capacitor 46. Because of the manner in which thepolarity directing diode 78 is poled, it blocks any current that mightotherwise flow therethrough so that the capacitive discharge currentwill all flow through the primary winding of the ignition coil 36.

The purpose of the inductor 72 and the by-pass diodes 74 and 76 is tolimit the current surge that might otherwise flow through the Triac 68,thus protecting it from being damaged. In the case where cylinder A isbeing fired, only one-half of the inductance 72 is in circuit with theTriac 68, the other half being by-passed by the diode 76. When it iscylinder B that is being fired, again only one-half of the inductance 72will be in circuit with the Triac 68 since diode 74 will serve as aby-pass for the other one-half of the inductance. The diodes 74 and 76when conducting permit current circulation through one-half of theinductor 72 to thereby allow any residual charge on capacitor 46 to bedissipated.

The voltage dividing networds 64 and 66 along with the capacitor 68 havean interesting affect on the discharge characteristics of the energystorage capacitors 46 and 48. Because the charge on the capacitor 68 isrelated to the time constant C X (R ee/R R,,,,), the charging of thecapacitor 68 lags behind that of the capacitor 46 or 48, whichever oneis being charged. When the engine is being cranked for starting or isrunning at a very low RPM, the release of energy from the coils of themagnetogenerator is lower than normal. Thus, the discharge of energyfrom the capacitors 46 or 48 will take place at a lower-"voltage levelsince the time constant is less of a factor on following the chargerate. Thus, the discharge of energy from the capacitors 46 or 48 willtake place at a lower voltage level since the time constant is less of afactor on following the charge rate. Thus, the presence of a sufficientvoltage to cause triggering is insured and provides a degree of timingretard, aiding in the ignition process at cranking. Once the engine RPMis at normal running or cruising speed, the charge rate of thecapacitors 46 and 48 stabilize, causing both a stabilization of timingadvance and a higher stored voltage level prior to the triggering of thedischarge control circuit.

Referring again to the polarity determining circuits 56 and 58,depending upon which cylinder is being fired, one or the other will actas a low impedance circuit for the primary winding of the ignition coilbeing energized, thus allowing the discharge current to continue to flowin a unidirectional manner until the energy is completely transferred tothe secondary winding of the ignition coil, thus completing thedischarge period at the plug gap. The resistors 80 and 84 can be chosento restrict the period of discharge to any desired value.

Due to the continuing current flow from the coils l8 and 20 of themagneto-generator (depending upon which coil has its associated breakerpoints open), the Triac 68 remains in conduction to prevent a furthertransfer of energy to the ignition coil until the charge on thecapacitor 46 or 48 has been dissipated.

Various modifications may be made to the circuit of FIG. 2 dependingupon the type of magneto-generator employed. More specifically, theembodiments of FIGS. 1 and 2 were described in connection with amagneto-generator arrangement which produced a positive voltage on theouter conductors 24 and 28. If the magneto-generator employed was of thetype producing a positive voltage on conductor 24 and a negative voltageon conductor 28, it would not be necessary to use a bidirectionalcurrent switching device such as a Triac but instead a unidirectionaldevice such as a SCR could be used. Further, in this latter arrangement,it would be necessary to reverse the direction of the diode 82. If themagneto-generator employed was of the type to produce a negative voltageon both conductors 24 and 28, again a bidirectional semiconductorswitching device such as a Triac would be necessary, but in thisinstance each of the diodes 78 and 82 shown in FIG. 2 would be reversedin polarity.

Still another modification permits the use of the present inventionwitha single cylinder internal combustion engine. In this arrangement,the voltage divider comprised of resistors 64 and 66 would be connectedbetween the conductor 24 and the ground bus 22 as would the inputelectrode of the Triac 68. The polarity directing diode would be poledsuch that its cathode would be connected to the conductor 40.

When a special type of spark plug is employed in the system of FIG. 1,it is sometimes undesirable to fire the plug off-cycle, i.e., due to thereverse generation of the magneto-generator when the cylinder is not ina charged condition, but when the points are still open. The solidlinewaveform illustrated in FIG. 3 shows the normal opencircuit voltageoutput of a given one of the magneto-generator coils 18 or 20. Thedotted-line shows the effect on the generated waveform when the pointsclose. Normal firing will take place somewhere in zone F during thepositive cycle of the generated waveform. A negative going spike (shownby the shaded portion of FIG. 3) may be produced just before the pointsclose at C. Further positive and negative going excursions are shortedout by the closed points. To suppress the negative going excursion justprior to the time of point closure, the circuit of FIG. 4 may beincluded. This circuit operates in a conventional fashion to clamp thenegative going excursion at ground.

While the triac devices are, to a certain extent, devices with built-intriggering features, it is sometimes desirable to utilize a discretetriggering device in the signal input to the triac. For this purpose,either a diac or Zener diode may be utilized to obtain a repeatablethreshold point in the circuit.

Although the present invention has been described to a certain degree ofparticularity, it should be understood that the present disclosure hasbeen made only by way of example and that numerous changes in thedetails of circuitry and the combination and arrangement of parts andelements (some of which have been suggested) may be resorted to withoutdeparting from the scope and spirit of the present invention.

1 claim:

1. In an ignition system for a two-cylinder internal combustion engineof the type having for each cylinder an ignition coil cooperating with amagneto-generator for producing a current in said coils, a set of camoperated breaker points for periodically coupling the current flow fromsaid magneto-generator to said ignition coils and thereby producing ahigh voltage pulse for delivery to the spark plugs, the improvementcomprising;

a. first and second energy storage devices having two terminalsconnected in series between said magneto-generators and said ignitioncoils;

b. first and second unidirectional current conducting devices connectedin series with said first and second energy storage devices and saidmagnetogenerators for causing said first and second energy storagedevices to be charged with a predetermined polarity;

c. a discharge control circuit adapted to be alternately connectedbetween said first energy storage device and one of said ignition coilsand the second energy storage device and the other of said ignitioncoils by means of said breaker points, for alternately controlling thedischarge of said first and second energy storage devices through itsassociated ignition coil; and

d. said discharge control circuit comprising:

1. a voltage divider connected in parallel with the magneto-generatorsassociated with said two cylinders;

2. a semiconductor switching device having an input electrode, andoutput electrode and a control electrode;

3. means connecting said input and output electrodes to one terminal ofsaid first and second energy storage devices respectively; and

4. means connecting said control electrode to said voltage divider suchthat when the voltage applied to said control electrode exceeds apredetermined threshold, one of said energy storage devices isdischarged through a path including said semiconductor switching device,one of said ignition coils and the breaker points associated with theother of said ignition coils.

2. An ignition system for a two-cylinder internal combustion enginecomprising in combination:

a. a first terminal, a second terminal and a grounded terminal;

b. a first magneto-generator coil connected between said first terminaland said ground terminal;

0. a second magneto-generator coil connected between said secondterminal and said grounded ter minal;

d. first and second sets of cam actuated breaker points connected inparallel with said first and second mangeto-generator coils;

e. capacitor means connected in parallel with said first and second setsof breaker-points;

f. a first energy storage device and a first unidirectional currentconducting device connected in series between said first terminal andsaid grounded terminal;

g. a second energy storage device and a second unidirectional currentconducting device connected in series between said second terminal andsaid grounded terminal;

h. a first autotransformer type ignition coil connected in parallel withsaid first unidirectional current conducting device and a secondautotransformer type ignition coil connected in parallel with saidsecond unidirectional current conducting device; and

i. a discharge control circuit connected between said first and secondterminals;

j. said discharge circuit comprising:

1. a semiconductor current control means having an input electrodeconnected to said first terminal, and an output electrode connected tosaid second terminal and a control electrode;

2. a voltage dividing network connected between said first and secondterminals; and

3. means connecting said control electrode to said voltage dividingnetwork.

UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECHQN PATENT NO. i3,884,207

DATED 3 May 20, 1975 'NVENTOWS) Andrew Kuehn III it is certified thaterror appears in the ab0veidentified patent and that said Letters Patentare hereby corrected as shown below:

Column 5, line 28, after "circulating" insert current Column 8, line 30,in Claim 2, sub-paragraph d, the word "mangeto" should read magnetofiigned and gealed this fif D3) 0% August1975 [SEAL] Arrest:

RUTH C. MASON C. MARSHALL DANN M K 11 1 Commissioner ufluu'ms andTrademarks

1. In an ignition system for a two-cylinder internal combustion engineof the type having for each cylinder an ignition coil cooperating with amagneto-generator for producing a current in said coils, a set of camoperated breaker points for periodically coupling the current flow fromsaid magneto-generator to said ignition coils and thereby producing ahigh voltage pulse for delivery to the spark plugs, the improvementcomprising; a. first and second energy storage devices having twoterminaLs connected in series between said magneto-generators and saidignition coils; b. first and second unidirectional current conductingdevices connected in series with said first and second energy storagedevices and said magneto-generators for causing said first and secondenergy storage devices to be charged with a predetermined polarity; c. adischarge control circuit adapted to be alternately connected betweensaid first energy storage device and one of said ignition coils and thesecond energy storage device and the other of said ignition coils bymeans of said breaker points, for alternately controlling the dischargeof said first and second energy storage devices through its associatedignition coil; and d. said discharge control circuit comprising:
 1. avoltage divider connected in parallel with the magnetogeneratorsassociated with said two cylinders;
 2. a semiconductor switching devicehaving an input electrode, and output electrode and a control electrode;3. means connecting said input and output electrodes to one terminal ofsaid first and second energy storage devices respectively; and
 4. meansconnecting said control electrode to said voltage divider such that whenthe voltage applied to said control electrode exceeds a predeterminedthreshold, one of said energy storage devices is discharged through apath including said semiconductor switching device, one of said ignitioncoils and the breaker points associated with the other of said ignitioncoils.
 2. a semiconductor switching device having an input electrode,and output electrode and a control electrode;
 2. a voltage dividingnetwork connected between said first and second terminals; and
 2. Anignition system for a two-cylinder internal combustion engine comprisingin combination: a. a first terminal, a second terminal and a groundedterminal; b. a first magneto-generator coil connected between said firstterminal and said ground terminal; c. a second magneto-generator coilconnected between said second terminal and said grounded terminal; d.first and second sets of cam actuated breaker points connected inparallel with said first and second mangeto-generator coils; e.capacitor means connected in parallel with said first and second sets ofbreaker points; f. a first energy storage device and a firstunidirectional current conducting device connected in series betweensaid first terminal and said grounded terminal; g. a second energystorage device and a second unidirectional current conducting deviceconnected in series between said second terminal and said groundedterminal; h. a first autotransformer type ignition coil connected inparallel with said first unidirectional current conducting device and asecond autotransformer type ignition coil connected in parallel withsaid second unidirectional current conducting device; and i. a dischargecontrol circuit connected between said first and second terminals; j.said discharge circuit comprising:
 3. means connecting said controlelectrode to said voltage dividing network.
 3. means connecting saidinput and output electrodes to one terminal of said first and secondenergy storage devices respectively; and
 4. means connecting saidcontrol electrode to said voltage divider such that when the voltageapplied to said control electrode exceeds a predetermined threshold, oneof said energy storage devices is discharged through a path includingsaid semiconductor switching device, one of said ignition coils and thebreaker points associated with the other of said ignition coils.